Presence of @id affects processing?

The 1.1 lang spec for <fn/> says that the presence of the ID attribute on <fn/> affects how the footnote is rendered. Is that true?
 
If so, I think we need to mention it in the ID attribute section of the archspec. I'm imagining a tool vendor providing an option to "automatically generate IDs", not knowing that the presence of the ID attribute has processing implications.
 
Are there other elements for which the presence of @id has any effect, whatsoever?
 
 
 
source: http://docs.oasis-open.org/dita/v1.1/CD01/langspec/langref/fn.html
 
 
-seth